Optics of Si/SiO2 superlattices: Application to Raman scattering and photoluminescence measurements

Abstract

A quantitative model of a Si/SiO2 superlattice (SL) is developed and applied to Raman and photoluminescence (PL) measurements. By analyzing the experimental reflection spectra of Si/SiO2 SLs on Si and Al substrates, we obtained optical parameters of amorphous Si layers with thickness below 4 nm. Both refractive index and extinction coefficient are found to decrease with Si-layer thickness, and this behavior reflects interaction of the Si network and the oxide surrounding. Interference-induced modification of Raman scattering and PL is quantitatively studied for Si/SiO2 SLs on Si and Al substrates, and the developed optical model describes well all observed features. PL spectra of the Si/SiO2 SLs are found to change under Ar+-laser irradiation, and this effect of laser annealing becomes stronger for thinner Si layers. For 1-nm-thick Si layers, a prolonged laser exposure decreases the PL intensity at 550 nm by a factor of 10 and red-shifts its maximum by about 50 nm, which indicates essential reorganization of the network under laser irradiation.

(Invited) Optical and Structural Properties of Silicon Nanocrystals and Laser-Induced Thermal Effects

“…A similar spectrum is measured for the asgrown Si/SiO 2 SLs where silicon excess is located in amorphous Si layers. For very small Si excess in SiO x films (x a 1.9) and very thin Si layers (a1 nm) in Si/SiO 2 SLs, the characteristic 470 cm 1 phonon band is not seen in the Raman spectra (10,13,17), i.e. no properly coordinated (elemental) silicon is present, and this is consistent with the optical properties of these samples.…”

“…Studies of Si-nc embedded in silica have been stimulated by reports on optical gain in this material (3,4). The mechanism of the red photoluminescence (PL) around 1.5 eV is still under debate, and several models have been proposed (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21). The PL spectrum of Si-nc embedded in silica matrix is independent of the crystallite size, which supports a "surface-state model" (6).…”

“…no properly coordinated (elemental) silicon is present, and this is consistent with the optical properties of these samples. It was estimated that amorphous Si and SiO 2 layers are separated by a0.8-nm-thick suboxide interfaces with n = 2 and very low absorption (13). The PL spectra of the as-grown MBD samples has a maximum at about 1.7 -1.8 eV (see Fig.…”

Two-step ball-milling synthesis of a Si/SiOx/C composite electrode for lithium ion batteries with excellent long-term cycling stability

“…It displays a broad peak at around 491 cm À1 , which is ascribed to the Si/SiO x nanoparticles, in which nanosilicon uniformly exists in SiO x particles. 28,29 What is more, the two characteristic Raman peaks at 1348 cm À1 and 1576 cm À1 are observed, which are the D-band for the disordered mode and the G-band for the stretching mode of C-C bonds of graphite. 30,31 Generally, the intensity ratio of D band to G band (I D /I G ) is used to estimate the degree of disorder in graphite.…”

Ion and electron irradiation-induced effects in nanostructured materials

“…Since this way of synthesizing embedded nanoclusters has been recently reviewed elsewhere, 75 we will not review the fabrication of nanoclusters with implantation in detail, but instead dwell on the ion modification of nanoclusters and nanoparticles after they have been synthesized. Also, it is important to know that embedded clusters can also be made with a variety of other techniques, such as thermal decomposition of thin grown layers 641,642 or cosputtering. 643 Regardless of synthesis method, the end result is typically roughly spherical nanoclusters with sizes ranging from a couple of nm ͑even smaller nanoclusters may exist, but are very difficult to detect͒ to hundreds of nanometers.…”